This invention relates to a new yeast strain and to a process for producing maltase therewith utilizing, as a carbon source, sucrose.
Maltase (.alpha.-glucosidase, EC 3.2.1.20) is an enzyme presently used in clinical assays for amylase. The maltase is utilized in an intermediate reaction wherein maltose, formed by the action of amylase on an oligosaccharide, is converted to glucose. The glucose is subsequently measured to determine the amylase activity. Presently, maltase is produced from yeast strains such as Saccharomyces cerevisae or Saccharomyces italicus. The maltase produced from Saccharomyces italicus is particularly useful in the assay for amylase in that it will not degrade higher oligosaccharides. Unfortunately, the carbon source is the growth medium for Saccharomyces italicus is maltose which is very expensive as compared to possible alternative carbon sources. Attempts to substitute relatively inexpensive sucrose or glucose as the carbon source have proven ineffective with Saccharomyces italicus, since regulatory controls in the yeast cells block maltase production when utilizing any other carbon source. Also, contaminating amounts of glucose sometimes present in commercial batches of maltose can have a deleterious effect on maltase production. In addition, the use of maltose as a carbon source has presented production difficulties since the activity of the maltase produced peaks just before the maltose in the medium is depleted thereby requiring that the cells be harvested within a relatively narrow time span.
Accordingly, it would be desirable to provide a means for producing maltase useful in clinical assays for amylase from a yeast strain which does not require maltose as the carbon source. Furthermore, it would be desirable to provide such a means which permits the use of inexpensive sucrose as the carbon source. Furthermore, it would be desirable to provide such a means wherein the activity of the maltase produced is not sharply reduced within a short time span so that the timing of cell harvesting is far less critical than in presently available processes.